This invention relates to apparatus used in offshore oil and gas operations. With more specificity, this invention relates to apparatus for the protection of the subsea wellheads of offshore wells.
In relatively shallow offshore waters, wells are drilled from bottom-supported drilling rigs such as jackup rigs. When such wells are completed, the completion can often be carried out by a surface wellhead mounted on some sort of production structure, for example a standalone well caisson. The wellhead equipment for such wells is very similar to equipment on onshore wells or platform wells.
In deeper waters, however, wells must be drilled with floating drilling rigs such as semi-submersibles and drill ships. Exploratory wells drilled in deeper waters are often simply plugged and abandoned. However, current technology permits many of such wells to be xe2x80x9csalvagedxe2x80x9d in the sense that the wells are eventually completed and tied back to a production facility, in a so-called xe2x80x9csubsea completion.xe2x80x9d
A typical sequence is that after the well has been drilled and all logging, testing and the like is complete, the well must be temporarily xe2x80x9cabandonedxe2x80x9d for a period of time, while the drilling rig moves off, and until the well can be completed. Often, additional wells are drilled to delineate a field, and if economically justified all of the temporarily abandoned wells are completed and tied back to a production facility.
The temporary abandonment is usually accomplished by setting mechanical and/or cement plugs in the wellbore. However, while such plugs effectively isolate the wellbore from the environment, the subsea wellhead, which rests on and protrudes above the sea floor, is left exposed and unprotected. Protection of the subsea wellhead is essential, as it has multiple seal surfaces and outer profiles which must remain undamaged for a subsea production assembly to be mounted atop the wellhead. Possible sources of damage include corrosion from the immersion in sea water; objects falling onto the subsea wellhead and scarring the various surfaces; or damage by objects falling on or otherwise striking the wellhead, such as boat anchors and the like.
Past efforts have been implemented to protect the subsea wellhead with various types of protectors which fit over the wellhead. Prior art subsea wellhead protectors have been made of metals of different sorts. While such protectors may be effective, their great weight requires that they be run using the drilling rig to lower the protector in place, usually on a string of drill pipe. This requirement means that expensive rig time must be devoted to the placement of metal protectors.
A tremendous economic incentive exists for a subsea wellhead protector which can be run without requiring use of a drilling rig, for example by use of a subsea Remotely Operated Vehicle (xe2x80x9cROVxe2x80x9d), which may be deployed from the rig while still in place over the well, yet frees the rig to do other tasks such as pulling anchors. Alternatively, it is desirable to have a wellhead protector which could be placed by an ROV deployed from a ship or other vessel, without a rig on location.
The present invention is a subsea wellhead protector having a minimum of metal components, with most of the protector formed from an elastomer such as polyurethane. The result is a light weight yet strong wellhead protector, which does not require a rig to hoist it and set it in place atop a subsea wellhead, but instead can be placed atop the subsea wellhead with an ROV.